The invention relates to a method of making a preform for internal high-pressure metal forming, as well as to a preform produced by the method. The invention further relates to a method for producing a body from the preform, and to a body produced by the method.
It is known to shape tubular metal objects by "hydroforming": for example reference can be made to EP-A-0620056, which shows how a tubular body is assembled from a number of tube sections to form a preform. In "hydroforming", ie. internal high-pressure forming, the tube is deformed by subjecting the interior of the tube to pressure, usually hydraulic pressure, so that it is permanently deformed and is pressed against a mold surrounding the tube. This process is basically known.
Tubular preforms used hitherto have enabled a multitude of essentially tubular bodies to be shaped by subjecting the preform to internal high-pressure forming. However, there exists a need for other kinds of bodies, eg. containers, and in particular fuel tanks, which hitherto have not been produced by internal high-pressure forming. At present, fuel tanks made of metal are formed from two deep-drawn halves each having a peripheral flange. The halves are positioned with their flanges in register, and are joined together in a sealed manner by roller seam welding at the flanges. Although this method of manufacture yields good results, one drawback is the space taken up by the welded flange extending around the tank. For technical reasons associated with the welding, this flange must have a certain width. Also, the shape of the tank is subject to restrictions due to the minimum radii which are imposed.
Besides containers, it may be disadvantageous for other bodies, such as supports for example, if their design is restricted to a tubular cross-section.
Therefore, the problem which poses itself is to extend the use of internal high-pressure metal forming to non-tubular bodies, in particular containers and supports. A further problem which is posed is to provide a fuel tank made of metal which achieves the best possible ratio between overall dimensions and capacity and on which in particular the peripheral flange is extremely small or non-existent.